NASHVILLE (AP) — A federal judge on Tuesday slightly tweaked his order requiring Knox County schools implement a school mask mandate, saying officials would be allowed to approve exemptions on a case by case basis.

In his 14-page ruling, however, U.S. District Judge J. Ronnie Greer warned school officials — who had previously refused to adopt a mask mandate amid the COVID-19 outbreak — that the new mask exemption policy must not be abused.

"The court reminds the Knox County Board of Education that its school system is no longer under a voluntary mask mandate; rather, it is under a court-ordered mask mandate," Greer wrote. "The record evidence supports the need for — and the court ordered — a universal mask mandate, and the court fully expects its mask mandate to be exactly that: universal, to every possible extent, with 'very few' medical exemptions ..."

The Knox County Board of Education must file monthly status reports which identify not only the number of exemptions for students, employees and visitors, but also the specific reasons for the exemptions. Greer added that he would impose "considerable sanctions" if the education board did not comply with his latest order.

Earlier this month, Knox County school officials asked Greer to loosen exemptions surrounding his school mask mandate, arguing that they needed more flexibility in determining who needs a mask.

Greer had ruled that schools in Knox County immediately adopt a mask mandate to help protect children with health problems more susceptible to the coronavirus pandemic. Notably, he only permitted narrow exemptions — allowing only students with autism or tracheotomy to not wear a mask while in school. He also blocked Republican Gov. Bill Lee's executive order allowing parents to opt out of school masks mandates from being enforced.

The ruling was one of three similar decisions where federal judges put a pause on Lee's order for three counties. Families and advocates across the state have challenged the policy in a handful of lawsuits amid spiking virus case numbers in schools.

Yet in Knox County, which includes Knoxville, the order sparked heated protests from those who opposed mask mandates and other COVID-19 precautions. Some students have faced adults calling them "sheep" while wearing a mask as at least one Republican state lawmaker encouraged families to "make a stand" and defy Greer's order.

Knox County adopted a mask mandate during the 2020-21 school year but chose not to this year despite COVID-19 numbers remaining high throughout the region and among school-aged children.

Public health agencies say indoor mask-wearing is a key coronavirus-prevention tool. The federal Centers for Disease Control says masks don't pose health risks for children older than toddlers, and recommends them for schools since vaccines still aren't authorized for children younger than than 12.